Inter-band carrier aggregation is supported in a Long Term Evolution-Advanced, LTE-A, Release-11, Rel-11, Carrier Aggregation, CA, system. In order to avoid mutual interference between Time Division Duplexing, TDD, systems at adjacent frequencies, different TDD uplink/downlink configurations may be used for cells or Component Carriers, CCs, in different bands.
In the LTE-A system, there are required peak rates of the system, up to 1 Gbps in the downlink and 500 Mbps in the uplink, as significantly improved over a Long Term Evolution, LTE, system. It is thus necessary in the LTE-A system to extend a bandwidth available to a User Equipment, UE, that is, a plurality of consecutive or inconsecutive carriers served by the same evolved Node B, eNB are aggregated together to serve the UE concurrently for a desirable rate, as illustrated in FIG. 1. Each of the carriers aggregated together can be referred to as a component carrier, each cell can be a component carrier, and cells (component carriers) served by different eNBs can not be aggregated. In order to ensure the UE in the LTE system to be able to operate over each of the aggregated carriers, a bandwidth of each of the component carriers is no more than 20 MHz.
Carrier aggregation can be further categorized into intra-band CA and inter-band CA dependent upon the bands of the aggregated carriers, and in inter-band CA systems of the Rel-11 and later, different TDD uplink/downlink configurations can be used for cells in different bands in order to avoid interference to other TDD systems.
As illustrated in FIG. 2, a carrier 1 and a carrier 2 are in a band A, whereas a carrier 3 is in a band B, and a cell 1, a cell 2 and a cell 3 are cells respectively over the carrier 1, the carrier 2 and the carrier 3. TDD uplink/downlink configurations of the cell 1 and the cell 2 are the same, e.g., the uplink/downlink configuration 1, and a TDD uplink/downlink configuration of the cell 3 is different from those of the cell 1 and the cell 2, e.g., the uplink/downlink configuration 2. When the carriers are aggregated for the UE in these three cells, such a situation may arise that the TDD uplink/downlink configurations of the cells aggregated for the UE are different.
In the LTE system, a radio frame is defined as 10 ms including ten sub-frames, each of which is 1 ms. Seven TDD uplink/downlink configurations are defined for each TDD radio frame, as depicted in Table 1, where D represents a downlink sub-frame, U represents an uplink sub-frame, and S represents a special sub-frame of the TDD system. The special sub-frame includes a Downlink Pilot Time Slot, DwPTS, a Guard Period, GP, and an Uplink Pilot Time Slot, UpPTS.
TABLE 1Uplink/downlink configurations of the TDD systemUplink/Sub-frame index ndownlink configuration01234567890DSUUUDSUUU1DSUUDDSUUD2DSUDDDSUDD3DSUUUDDDDD4DSUUDDDDDD5DSUDDDDDDD6DSUUUDSUUD
The UE in the LTE-A TDD system needs to feed back ACK/NACK feedback information of a plurality of downlink carriers and downlink sub-frames in the same uplink sub-frame. Particularly the number of sub-frames for which the UE needs to feed back ACK/NACK in the same uplink sub-frame can be defined as M, where M takes different values in different uplink sub-frames and different uplink/downlink configurations, as depicted in Table 2, where a set of sub-frames for which ACK/NACK is fed back in the uplink sub-frame n includes sub-frames indexed n-k, and k represents the values in the set of {k0, k1, . . . , kM−1} corresponding to the uplink sub-frame indexed n in Table 2.
TABLE 2A set of indexes of downlink sub-frames corresponding to the uplink sub-frame in theTDD system, K: {k0, k1, . . . kM−1}Uplink/downlinkSub-frame index nconfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5, 4, 7——————5——13, 12, 9, 8, 7, 5, 4, 11, 6———————6——775——77—
In the LTE-A system, a Physical Uplink Control Channel, PUCCH, is transmitted only over a primary component carrier, and 2/3/4-bit ACK/NACK information can be transmitted through a scheme of PUCCH format 1b with channel selection, where different ACK/NACK feedback information states are distinguished by the UE selecting channel for transmission among a plurality of candidate channel resources. Particularly a mapping table is defined respectively for transmission of 2, 3 or 4-bit ACK/NACK to map the different ACK/NACK information state to be fed back to real transmission information (i.e. one of four Quadrature Phase-Shift Keying, QPSK, constellation points transmitted by PUCCH format 1b) and the transmission channel resources. 2, 3 and 4 PUCCH format 1a/1b channel resources are required respectively for the 2, 3 and 4-bit ACK/NACK feedback information in a transmission mode via a single antenna port.
In the LTE-A TDD system, since transmission of at most 4 bits of ACK/NACK information is supported in the scheme of PUCCH format 1b with channel selection, the use of this scheme to transmit ACK/NACK information is supported at present only for the UE for which no more than two carriers are aggregated, and when the UE needs to feed back more than 4 bits ACK/NACK in an uplink sub-frame, the ACK/NACK information needs to be bundled to lower the number of bits of the ACK/NACK feedback information, and a particular transmission scheme is as follows:
A. With M=1 or 2 corresponding to the current uplink sub-frame n:
With M=1, no spatial bundling is required for multi-codeword ACK/NACK; in a transmission mode configured for two aggregated carriers, A=2 bits of ACK/NACK information needs to be fed back when both of the carriers are in a uni-codeword transmission mode, A=3 bits of ACK/NACK information needs to be fed back when one of the carriers is in a multi-codeword transmission mode and the other carrier is in the uni-codeword transmission mode, and A=4 bits of ACK/NACK information needs to be fed back when both of the carriers are in the multi-codeword transmission mode; and a mapping relationship of a sequence of ACK/NACK information to be fed back generated by the UE HARQ-ACKju0), . . . , HARQ-ACK(j), . . . HARQ-ACK(A−1) to respective transport blocks/sub-frames and downlink carriers is as depicted in Table 3, where 0≦j≦A−1, Aε[2,3,4], and the UE generates NACK/DTX as feedback information for respective transport blocks/sub-frames in which no data is received; and the UE maps PUCCH resources corresponding to the respective carriers (cells) into A PUCCH resources in an ascending order of j in Table 3.
TABLE 3A mapping relationship of a sequence of ACK/NACK informationto be fed back to respective transport blocks/sub-frames anddownlink carriers with M = 1 (mapping of transport blocks and serving cells to HARQ-ACK(j) for PUCCHformat 1b HARQ-ACK channel selection with M = 1)HARQ-ACK(j)HARQ-HARQ-HARQ-HARQ-AACK(0)ACK(1)ACK(2)ACK(3)2TB1 PrimaryTB2 SecondaryNANAcellcell3TB1 ServingTB2 ServingTB3 ServingNAcell1cell1cell24TB1 PrimaryTB2 PrimaryTB3 SecondaryTB4 Secondarycellcellcellcell
With M=2, spatial bundling is required for multi-codeword ACK/NACK, and the UE feeds back A=4 bits of ACK/NACK information all the time; and a mapping relationship of a sequence of ACK/NACK information to be fed back generated by the UE HARQ-ACK(0), . . . , HARQ-ACK(j), . . . HARQ-ACK(A−1) to respective sub-frames and downlink carriers is as depicted in Table 4, where 0≦j≦A−1, A=4, and the UE generates NACK/DTX as feedback information for respective sub-frames in which no data is received; and the UE maps PUCCH resources corresponding to the respective carriers (cells) into A PUCCH resources in an ascending order of j in Table 4.
TABLE 4A mapping relationship of a sequence of ACK/NACK informationto be fed back to respective sub-frames over respectivecarriers with M = 2 (mapping of sub-frames on respectiveserving cells to HARQ-ACK(j) for PUCCH format 1b HARQ-ACK channel selection for TDD with M = 2)HARQ-ACK(j)HARQ-HARQ-HARQ-HARQ-AACK(0)ACK(1)ACK(2)ACK(3)4The firstThe secondThe firstThe secondsubframe ofsubframe ofsubframe ofsubframe ofPrimary cellPrimary cellSecondary cellSecondary cell
In order to make a feedback, the channel resources nPUCCH,i(1), 0≦i≦A−1 need to be determined particularly as follows: for an SPS PDSCH, a semi-static PUCCH format 1b resource is determined from a Transmit Power Control, TPC, field in a PDCCH instructing the SPS PDSCH to be activated; for a Physical Downlink Shared Channel, PDSCH, with a corresponding Physical Downlink Control Channel, PDCCH, or a PDCCH instructing a Semi-Persistent Scheduling, SPS, resource to be released, transmitted over a primary component carrier, an implicit PUCCH format 1b resource is determined from the lowest Control Channel Element, CCE, index occupied by the PDCCH, and with M=1 and in the multi-codeword transmission mode, another implicit PUCCH format 1b resource is further determined from the CCE+1 in correspondence to the second Transport Block, TB, in the sub-frame; and for a PDSCH transmitted over a secondary component carrier, if its corresponding PDCCH is transmitted over the primary component carrier, then again an implicit PUCCH format 1b resource is determined from the lowest CCE of the PDCCH, and with M=1 and in the multi-codeword transmission mode, another implicit PUCCH format 1b resource is further determined from the CCE+1 in correspondence to the TB2, whereas if its corresponding PDCCH is transmitted over a secondary component carrier, then a set of semi-statically configured PUCCH format 1b resources is determined from a TPC field in the PDCCH (with M=1 and in the multi-codeword transmission mode, or with M=2, each set of resources includes two resources; otherwise, each set of resources includes one resource);
With M=1 or 2 corresponding to the sub-frame n above, the UE refers to the ACK/NACK mapping table with A=2, 3 or 4 (see Tables 10.1.3.2-1, 10.1.3.2-2 and 10.1.3.2-3 in TS36.213, Section 10.1.3.2) by the current sequence of ACK/NACK information to be fed back HARQ-ACK(0), . . . , HARQ-ACK(j), . . . , HARQ-ACK(A−1) and transmits corresponding PUCCH format 1b carried information b(0)b(1) over a PUCCH resource nPUCCH(1) selected among the A PUCCH resources nPUCCH,i(1) by using PUCCH format 1b, where 0≦i≦A−1, Aε[2,3,4].
B. With M=3 or 4 corresponding to the current uplink sub-frame n:
Spatial bundling is required for multi-codeword ACK/NACK, but the spatially-bundled feedback information bits are still more than four bits and need to be bundled in the time domain, where under the principle of time-domain bundling, 2 bits of bundled information corresponding to each downlink carrier represents the number of sub-frames received consecutively and correctly starting with a first scheduled sub-frame over the downlink carrier, that is, the UE generates for each downlink carrier a sequence of M-bit ACK/NACK information to be fed back HARQ-ACK(0), . . . , HARQ-ACK(j), . . . , HARQ-ACK(M−1), for which nPUCCH,i(1) PUCCH format 1b resources are occupied, where 0≦j≦M−1, 0≦i≦3; and the UE generates NACK/DTX as feedback information for respective sub-frames in which no data is received.
For a primary component carrier, if there is an SPS PDSCH, then its feedback information is mapped to HARQ-ACK(0), and its corresponding PUCCH format 1b resource is mapped to nPUCCH,0(1), and the remaining HARQ-ACK(j) with 1≦j≦M−1 represents feedback information of a downlink sub-frame corresponding to a PDCCH with the Downlink Assignment index, DAI, value of “j” transmitted over the primary component carrier, and nPUCCH,i(1) represents an implicit PUCCH format 1b resource derived from the lowest CCE of a PDCCH with the DAI value of 1; or if there is no SPS PDSCH, then HARQ-ACK(j) with 0≦j≦M−1 represents feedback information of a downlink sub-frame corresponding to a PDCCH with the DAI value of “j+1” transmitted over a primary cell, and nPUCCH,0(1) and nPUCCH,1(1) represent implicit PUCCH format 1b resources derived from the lowest CCEs of PDCCHs with the DAI values of 1 and 2 respectively.
For a secondary component carrier, HARQ-ACK(j) with 0≦j≦M−1 represents feedback information of a downlink sub-frame corresponding to a PDCCH with the DAI value of “j+1” transmitted over the secondary component carrier, and when a PDCCH scheduling a secondary component carrier is transmitted over a primary component carrier, nPUCCH,2(1) and nPUCCH,3(1) represent PUCCH format 1b resources derived from the lowest CCE indexes of PDCCHs, with the DAI values of 1 and 2, scheduling data over the secondary component carrier, respectively; and when a PDCCH scheduling a secondary component carrier is transmitted over a secondary component carrier, nPUCCH,2(1) and nPUCCH,3(1) represent PUCCH format 1b resource determined from ACK/NACK resource indication information carried by TPC fields in PDCCHs, with the DAI values of 1 and 2, scheduling data over the secondary component carrier, respectively, where the indication information indicates one of a plurality of sets of channel resources preconfigured for the UE in higher-layer signaling, and each set of channel resources includes at least two PUCCH format 1b resources.
The UE refers to the corresponding ACK/NACK mapping table with M=3 or 4 for time-domain bundling (see Tables 10.1.3.2-5 and 10.1.3.2-6 in TS36.213, Section 10.1.3.2) by the sequences of ACK/NACK information to be fed back corresponding respectively to the primary component carrier and the secondary component carriers and transmits corresponding PUCCH format 1b carried information b(0)b(1) over a PUCCH resource nPUCCH(1) selected among the M PUCCH resources nPUCCH,i(1) using PUCCH format 1b, where 0≦j≦M−1, Mε[3,4].
Since only transmission of a PUCCH over a Primary Component Carrier, PCC, is supported, when different TDD uplink/downlink configurations are used for two carriers aggregated for the UE, the direction of a sub-frame with the same index may be different over a Secondary Component Carrier, SCC, from the direction thereof over a PCC. In order to ensure transmission of ACK/NACK feedback information of a downlink sub-frame over a secondary component carrier, a timing relationship for the UE to report ACK/NACK feedback information of downlink data of the secondary component carrier (simply a DL HARQ timing) needs to be determined again, and this timing relationship is a correspondence relationship of ACK/NACK feedback information of a downlink sub-frame over the secondary component carrier to an uplink sub-frame in which ACK/NACK feedback information of the downlink sub-frame is transmitted, so that ACK/NACK feedback information of the downlink sub-frame over the secondary component carrier can be transmitted in the uplink sub-frame over the primary component carrier. At this time an uplink sub-frame for an ACK/NACK feedback corresponding to a downlink sub-frame of the secondary component carrier may be determined for the secondary component carrier in a reference TDD uplink/downlink configuration and a correspondence relationship of downlink sub-frames to uplink sub-frames in the reference TDD uplink/downlink configuration (e.g., the set of k in the reference TDD uplink/downlink configuration in Table 2). The reference TDD uplink/downlink configuration may be the same as a TDD uplink/downlink configuration configured for the secondary component carrier in a System Information Block 1, SIB1, or may be the same as a TDD uplink/downlink configuration configured for the primary component carrier in the SIB1 or may be one of other existing uplink/downlink configurations different from both of the TDD uplink/downlink configurations configured for the primary component carrier and the secondary component carrier in the SIB1. At this time there may be different corresponding sets of sub-frames, transmitted over the primary component carrier and the secondary component carrier, for which ACK/NACK is fed back in the uplink sub-frame n of the primary component carrier and thus different numbers of sub-frames (numbers of bits of ACK/NACK feedback), over the primary component carrier and the secondary component carrier, for which ACK/NACK is fed back in the uplink sub-frame n, so there is no directly corresponding ACK/NACK mapping table; and when a PDSCH over the secondary component carrier is scheduled by a PDCCH transmitted over the primary component carrier, an implicit channel resource derived from the lowest CCE of the PDCCH may conflict with another sub-frame and/or another UE, so the scheme of PUCCH format 1b with channel selection in the Rel-10 can not be reused here.
As can be apparent, there has been absent so far a definite solution for feeding back ACK/NACK in aggregation of carriers with different uplink/downlink configurations.